Study Of Strong Coherent Interference Suppression

As a new security system for port defense, compared to the traditional diver detectionsonar, the multistatic diver detection sonar can get higher performance through its flexibledeployment strategy. The strong direct blast interference suppression in multistatic sonar isone of the key technologies to overcome. The strong direct blast interference suppression canbe seemed as a typical strong coherent interference. From the angles of coherent signalsdistinguishing and coherent interference suppression, the strong coherent interferencesuppression is discussed. The main results and achievements are summarized as follows:1. By analyzing deployment strategy of multistatic sonar, the mathematical model of thestrong coherent interference is built. The strong coherent interference in multistate sonar is akind of interference related with geometric configuration and work environment. When theangle between the interference and signal is different, the algorithm of direction of arrival iseffective. When the arriving time between the interference and signal is different, thealgorithm of pulse compression is effective. The first condition above is discussed in thethesis.2. The performances of subsistent algorithms for coherent signals distinguishingincluding convention beamforming, MUSIC algorithm based on spatial smoothing andMVDR algorithm based on spatial smoothing are analyzed. The performances of the threealgorithms are all related with the angle between interference and signal, the bandwidth of themain lobe, the height of the side lobe and interference-to-signal rate. These two algorithmsbased on spatial smoothing can get better resolution by breakthrough the limitations of thebandwidth of the main lobe and the height of the side lobe. But because of the hugecalculation and the sensitivity of the arrays, new limitations are brought to the practicalapplication at the same time.3. The performances of two coherent interference suppression algorithms based on zeroconstraint condition of beam pattern and using jamming matrix to preprocess the receivedsignal are analyzed. With the Least Squares thought and zero constraint condition used in thealgorithm, the zero indentation is formed in the direction of the coherent interference of thebeam pattern, so as to achieve the purpose of coherent interference suppression. Aiming at theinfluence on the zero constraint condition DOA algorithm, the array errors including phaseerror, amplitude error and array disturbance are analyzed. When the direction of the coherentinterference is next to the main lobe of target echo, the algorithm using jamming matrix to preprocess the received signal is proposed. Although the interference in the main lobe can besuppressed, accurate array model is required for the algorithm.4. The pool experiment of strong coherent interference suppression based on bistaticsonar is designed. The results show that, after the correction of arrays, the coherentinterference of the interference-to-signal rate at about36dB can be suppressed effectivelythrough the algorithm based on zero constraint condition of beam pattern. And the correctdirection is estimated.